1. Technical Field
The present invention relates to a linear motor that causes a linear motion to an object to be driven using electromagnetic force, and more particularly to a linear motor having a cooling structure.
2. Description of Related Arts
In general, a linear motor includes a field unit having a plurality of permanent magnets which are arranged such that the adjacent polarities are different from each other, and an armature which has a coil arranged opposite to the permanent magnets and which is capable of sliding in a longitudinal direction of the field unit.
In the linear motor, current flows through the coil of the armature so as to cross magnetic flux generated by the permanent magnets of the field unit, whereby driving force is generated on the coil in the longitudinal direction by electromagnetic induction to move the armature.
Since the coil generates heat during the operation of the linear motor, it is necessary to prevent the heat of the coil from being transferred to an object to be driven, such as a processing apparatus arranged on a movable stage. In view of this, a variety of cooling structures for cooling the armature of the linear motor have been developed.
As a technique with respect to cooling an armature of a linear motor, there has been disclosed a linear motor having a cooling passage folded successively in the moving direction of the armature in an intermediate plate which is provided between an armature mounting plate and a table, and in the armature mounting plate (see, for example, Japanese Unexamined Patent Publication No. 2004-304932; hereafter, Patent Document 1). A refrigerant flowing into the cooling passage flows from the intermediate plate and is discharged from the armature mounting plate.
Also, the applicant of the present application has proposed an armature for a linear motor, which is provided with a cooling pipe arranged in a plurality of slots of a core so as to sandwich a coil (see, for example, Japanese Unexamined Patent Publication No. 2008-35698; hereafter, Patent Document 2).
Meanwhile, the linear motor according to Patent Document 1 cools the inside of the slot by the cooling passage formed in the intermediate plate and in the armature mounting plate, whereby cooling efficiency is high.
However, since this linear motor according to Patent Document 1 has a large number of components forming the cooling structure, the production cost is increased, and it is difficult to realize high assembling precision.
In the linear motor according to Patent Document 2, two cooling pipes are arranged in the slot so as to sandwich the coil, whereby cooling efficiency is very high.
However, in the armature for the linear motor according to Patent Document 2, the cooling pipe is long, so the pressure loss of the refrigerant is large. Also, since the cooling pipe is present on the surface opposite to a magnet, it is difficult for a magnetic field of the coil to reach the permanent magnet, whereby the maximum thrust force is decreased. In addition, the cooling pipe in the slot has to be electrically insulated, whereby production cost is increased.
The present invention is made in view of the above circumstances and aims to provide a linear motor that is capable of reducing a pressure loss of a refrigerant, achieving efficient cooling by making a temperature distribution uniform, and increasing maximum thrust force by reducing a magnetic resistance.